Pre-mixes have been used in the manufacturing of brake pad friction materials for some time. Friction materials produced with a pre-mix tend to process quickly, and exhibit improved performance characteristics in the completed brake pad as compared with pads produced without a pre-mix. For example, brake pads formed of pre-mixed materials tend to exhibit improved noise/vibration/harshness characteristics.
Typically, friction materials include rubber, fiber, and filler components. Usually an intensive rubber mixer is needed to masticate the binder material(s) and thoroughly mix it in with the other raw materials. To begin, a first material is added to the mixer. After mixing, the first material may be granulated to a desired size by a chopper to form a pre-mix. This pre-mix is then transferred to a second mixer, where other raw materials are added to the pre-mix. The resulting mixture is then mixed to produce the final friction material. The friction material can subsequently be formed into brake pads or other friction material products through any of a variety of methods, such as compression molding, for example.
The pre-mixing process may be relatively inefficient. First, granulating the premix in between the first mixer and the second mixer can be laborious and costly. Second, the premix has a limited shelf-life due to the tendency of any chemical components of the pre-mix to cure within a short period of time.